1 The aim of this study was to investigate the effect of sertraline, a selective serotonin re-uptake inhibitor, on contractile responses to noradrenaline (NA), KCl, serotonin (5-HT) and electrical field stimulation of rat isolated vas deferens. 2 Pre-treatment with 10(-4) M sertraline showed inhibitory effects on responses to NA, KCI, 5-HT and electrical field stimulation, while pre-treatment with 10(-6) and 10(-5) M sertraline caused potentiation of responses to NA (10(-7) and 10(-6) M). 3 A voltage-dependent calcium channel activator, Bay K 8644, restored the inhibited responses when sertraline was washed out of the organ bath, although restoration could not be seen when sertraline was not removed. 4 The inhibition of the contractile responses by sertraline pre-treatment may be via a mechanism through calcium channels which is additional to the selective serotonin re-uptake inhibitory effect of sertraline.